Ink jet recording apparatus

ABSTRACT

An ink jet recording apparatus according to the invention includes an ink, and a discharge head that discharges the ink, in which the discharge head includes a plurality of pressure chambers respectively communicating with a plurality of nozzle holes formed in a nozzle plate, a vibration plate changing the capacity of each of the plurality of pressure chambers, and an ink supply chamber for supplying the ink to the plurality of pressure chambers, the capacity of the pressure chamber is 10.0×10 6  μm 3  or less, the density in which the plurality of nozzle holes are arranged in the nozzle plate is 200 dpi or more, the ink includes a dye, water, and an organic solvent, a ratio (organic solvent/water) of a mass of the organic solvent to a mass of the water in the ink is 0.3 to 0.7.

BACKGROUND

1. Technical Field

The present invention relates to an ink jet recording apparatus.

2. Related Art

An ink jet type recording apparatus, which is an example of a liquidejecting apparatus, includes a discharge head having a nozzle hole fordischarging an ink, driving means that causes an ink to be dischargedthrough the nozzle hole (for example, a piezoelectric vibrator, and aheating element), and control means that controls the driving means inaccordance with data. A supply of an ink to the nozzle hole is performedby, for example, an ink cartridge, an ink supply chamber that receivesan ink from the ink cartridge, and an ink supply channel that connectsthe ink supply chamber to the nozzle hole. The ink cartridge is commonlyreplaceable.

As an example of the discharge head, there is a discharge head thatincludes a nozzle plate provided with a nozzle hole, and a vibrationplate disposed in parallel with the nozzle plate and vibrated by apiezoelectric element, and that discharges an ink by changing the volumeof a pressure chamber formed between the nozzle plate and the vibrationplate using vibration of the vibration plate (for example,JP-A-8-020107).

JP-A-8-020107 discloses that when the apparatus is placed in a lowtemperature environment, if an ink starts to become frozen from thenozzle plate side, and the freezing reaches the vibration plate, thevibration plate or the piezoelectric element may be damaged, and thus,an effort is made to suppress damage to the vibration plate or thepiezoelectric element by adjusting the structure of the head, or arelative thermal capacity of a member to cause the ink to become frozenfrom the vibration plate side.

However, recently, definition required for an image of the ink jetrecording apparatus has been highly increased, and the discharge headhas been refined and densified in accordance with this increase.Therefore, it is difficult to prevent the damage or the like caused bythe freezing of ink in the discharge head only by improving thestructure or a material of the discharge head as the technologydisclosed in JP-A-8-020107. In other words, it is difficult to make thetemperature difference within the head due to miniaturization of thehead, and it is difficult to control the freezing starting point of theink.

SUMMARY

An advantage of some aspects of the invention is to provide an ink jetrecording apparatus which includes a highly dense and miniaturizeddischarge head, and of which the discharge head is hardly damaged or thelike, even when the apparatus is placed in a low temperatureenvironment.

The invention can be realized in the following aspects or applicationexamples.

Application Example 1

According to this application example, there is provided an ink jetrecording apparatus comprising an ink, and a discharge head thatdischarges the ink, in which the discharge head includes a plurality ofpressure chambers respectively communicating with a plurality of nozzleholes formed in a nozzle plate, a vibration plate changing the capacityof each of the plurality of pressure chambers, and an ink supply chamberfor supplying the ink to the plurality of pressure chambers, thecapacity of the pressure chamber is 10.0×10⁶ μm³ or less, and thedensity in which the plurality of nozzle holes are arranged in thenozzle plate is 200 dpi or more, and the ink includes a dye, water, andan organic solvent, a ratio (organic solvent/water) of a mass of theorganic solvent to a mass of the water in the ink is 0.3 to 0.7.

In this case, the ink jet recording apparatus includes a highly denseand miniaturized discharge head, and the discharge head is hardlydamaged due to the freezing of the ink, even when the apparatus isplaced in a low temperature environment. In other words, in this ink jetrecording apparatus, at least a part of volume expansion of water causedby solidification when the apparatus is placed in a low temperatureenvironment is offset by volume contraction of the organic solvent.According to this, it is possible to reduce stress which may damage thevibration plate or the piezoelectric element of the discharge head.

Application Example 2

In the ink jet recording apparatus according to Application Example 1,when the ink jet recording apparatus is cooled, and the ink is frozen,an ink of the nozzle plate side may be preferentially frozen to the inkof the vibration plate side within the pressure chamber.

Application Example 3

In the ink jet recording apparatus according to Application Example 1 or2, the pressure chamber and the vibration plate may not be substantiallyin contact with the air outside.

Application Example 4

In the ink jet recording apparatus according to any one of ApplicationExamples 1 to 3, Young's modulus of a material configuring the vibrationplate may be 250 Gpa or less.

Application Example 5

In the ink jet recording apparatus according to any one of ApplicationExamples 1 to 4, a flexible and elastic film may be included in aportion of a wall surface of the ink supply chamber.

In this case, even when the volume of the ink is expanded due to thefreezing, it is possible to alleviate the stress generated by theexpansion. According to this, even when the apparatus is placed in a lowtemperature environment, the damage to the discharge head caused by thefreezing of the ink hardly occurs.

Application Example 6

In the ink jet recording apparatus according to any one of ApplicationExamples 1 to 5, a volume expansion coefficient of the ink in a casewhere the ink is frozen under a temperature condition of −20° C. may be1.6% to 5.3%.

Application Example 7

In the ink jet recording apparatus according to any one of ApplicationExamples 1 to 6, the ink may include a resin component.

In this case, when the ink is frozen, since a rigid solid (an ice) ishardly generated by the freezing of water due to the presence of theresin component, but a sherbet-shaped (an ice cream-shaped) solid isgenerated, damage to the discharge head caused by the freezing of theink further hardly occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a partial cross-sectional perspective view of an ink jetrecording apparatus according to an embodiment.

FIG. 2 is an exploded perspective view schematically illustrating adischarge head according to the embodiment.

FIG. 3 is a cross-sectional schematic diagram of the main parts of thedischarge head according to the embodiment.

FIG. 4 is a cross-sectional schematic diagram of the main parts of thedischarge head according to the embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Some embodiments of the invention are described in the following. Theembodiments described below are examples of the invention. The inventionis not limited at all to the following embodiments, and includes variousmodification embodiments in a scope not departing from the gist of theinvention. In addition, the entirety of the configuration describedbelow is not necessarily the essential configuration of the invention.

1. Ink Jet Recording Apparatus

The ink jet recording apparatus according to the invention includes adischarge head discharging an ink. In the following, an ink jetrecording apparatus 200 having the discharge head is exemplarilydescribed, but the ink jet recording apparatus according to theinvention is not limited to this embodiment. The ink jet recordingapparatus of the invention is not limited to a shape or structure of theink jet recording apparatus 200 to be exemplified, and it can besuitably configured Hereinafter, the ink jet recording apparatus 200 isdescribed as one example. FIG. 1 is a perspective view schematicallyillustrating the ink jet recording apparatus 200 according to theembodiment.

The ink jet recording apparatus 200 includes a head unit 230, a drivingunit 210, and a control unit 260 as illustrated in FIG. 1. Further, theink jet recording apparatus 200 includes an apparatus main body 220, apaper feeding unit 250, a tray 221 in which a recording paper P isinstalled, a discharge port 222 for discharging the recording paper P,and an operation panel 270 disposed on an upper surface of the apparatusmain body 220.

The head unit 230 has an ink jet type recording head (hereinafter,simply referred to as a “head” or a “discharge head”) configured toinclude a discharge head 100 described below. The head unit 230 furtherincludes an ink cartridge 231 supplying an ink to the head, and acarrying unit (carriage) 232 on which the head and the ink cartridge 231are mounted.

The driving unit 210 can cause the head unit 230 to reciprocate. Thedriving unit 210 includes a carriage motor 241, which is a drivingsource of the head unit 230, and a reciprocating mechanism 242 whichcauses the head unit 230 to reciprocate by rotation of the carriagemotor 241.

The reciprocating mechanism 242 includes a carriage guide shaft 244 ofwhich both ends are supported by a frame (not illustrated), and a timingbelt 243 extending in parallel with the carriage guide shaft 244. Thecarriage guide shaft 244 supports the carriage 232, while allowing thecarriage 232 to reciprocate freely. Further, the carriage 232 is fixedto a portion of the timing belt 243. When an operation of the carriagemotor 241 runs the timing belt 243, the head unit 230 reciprocates beingguided by the carriage guide shaft 244. While the head unitreciprocates, an ink is discharged at a predetermined timing from thehead, and printing is performed on the recording paper P.

In the embodiment, an example is illustrated in which printing isperformed while both the discharge head 100 and the recording paper Pare being moved, but the ink jet recording apparatus may include amechanism in which printing is performed on the recording paper P whilepositions of the discharge head 100 and the recording paper P are beingrelatively changed. In addition, in the embodiment, an example in whichprinting is performed on the recording paper P is illustrated, but therecording medium on which printing can be performed by the ink jetrecording apparatus of the invention is not limited to paper, and a widerange of mediums such as a cloth, a film, a metal or the like can beexemplified as the recording medium, and it is possible to change theconfiguration appropriately.

The control unit 260 can control the head unit 230, the driving unit210, and the paper feeding unit 250. The paper feeding unit 250 can feedthe recording paper P from the tray 221 to the head unit 230 side. Thepaper feeding unit 250 includes a paper feeding motor 251, which is adriving source of the paper feeding unit, and a paper feeding roller 252rotated by an operation of the paper feeding motor 251. The paperfeeding roller 252 includes a driven roller 252 a and a driving roller252 b facing each other in the vertical direction with a feeding routeof the recording paper P interposed therebetween. The driving roller 252b is connected to the paper feeding motor 251. When the paper feedingunit 250 is driven by the control unit 260, the recording paper P is fedso as to pass a position below the head unit 230. The head unit 230, thedriving unit 210, the control unit 260, and the paper feeding unit 250are provided inside the apparatus main body 220.

In addition, the exemplified ink jet recording apparatus 200 has onedischarge head, and it can perform printing on the recording medium withthis discharge head. However, the ink jet recording apparatus may have aplurality of discharge heads. In a case where the ink jet recordingapparatus has a plurality of discharge heads, each of the plurality ofdischarge heads may be operated independently as described above, andthe plurality of discharge heads may be connected to each other to formone assembled head. As this assembled head, for example, a line-typehead in which all nozzle holes of the plurality of heads are arranged atuniform intervals can be exemplified.

The discharge head 100 mounted on the ink jet recording apparatus 200,and an ink is described below in order.

1.1. Discharge Head

The discharge head 100 of the embodiment includes a plurality ofpressure chambers 20 respectively communicating with a plurality ofnozzle holes 12 formed on a nozzle plate 10, a vibration plate 30changing each capacity of the plurality of pressure chambers 20, and anink supply chamber for supplying an ink to the plurality of pressurechambers 20.

FIG. 2 is a cross-sectional view schematically illustrating main partsof the discharge head 100 according to one example of the embodiment.FIG. 2 is an exploded perspective view of the discharge head 100, andillustrates the upside-down state of the discharge head mounted in theink jet recording apparatus 200 illustrated in FIG. 1. The exemplifieddischarge head 100 has a piezoelectric element 32, and the piezoelectricelement 32 is formed being in contact with the vibration plate 30. Inaddition, a piezoelectric actuator 34 is configured to include thepiezoelectric element 32 and the vibration plate 30. In addition, thescale of each configuration is properly changed for convenience ofdescriptions in the drawings. In addition, FIG. 2 illustrates thesimplified piezoelectric element 32.

The discharge head 100 includes the nozzle plate 10 having the nozzlehole 12, a pressure chamber substrate 120 for forming the pressurechamber 20, and the piezoelectric element 32 as illustrated in FIG. 2.Further, the discharge head 100 may have a housing 130 as illustrated inFIG. 2.

The nozzle plate 10 has the nozzle hole 12 as illustrated in FIG. 2. Anink can be discharged from the nozzle hole 12. A plurality of nozzleholes 12 is provided by being arranged on the nozzle plate 10. Thenumber of nozzle holes 12 provided in the nozzle plate 10 is notparticularly limited. In the discharge head 100 of the embodiment, a gapin which the nozzle holes 12 are arranged is 200 dpi or more. In otherwords, a gap between the arranged adjacent nozzle holes 12 is 127 μm orless. As a material of the nozzle plate 10, for example, silicon, astainless steel (SUS) or the like can be exemplified. In addition, as amaterial of the nozzle plate 10, an alloy including iron (Fe) as a maincomponent (50% or more), and chromium (Cr) in an amount of 10.5% or moreis more preferable, since it is possible to obtain rigidness and rustresistance at the same time.

In the discharge head 100, the pressure chamber substrate 120 isprovided being in contact with the nozzle plate 10. As a material of thepressure chamber substrate 120, for example, silicon or the like can beexemplified. The pressure chamber substrate 120 partitions a spacebetween the nozzle plate 10 and the vibration plate 30, and thus the inksupply chamber 40 (a liquid storage unit), a supply port 126communicating with the ink supply chamber 40, and the pressure chamber20 communicating with the supply port 126 are formed as illustrated inFIG. 2.

In this example, the ink supply chamber 40, the supply port 126, and thepressure chamber 20 are described separately, but they are all liquidchannels. As long as the pressure chamber 20 is formed, it does notmatter how the channel is designed. In addition, for example, in theillustrated example, as the supply port 126, a portion of the channel isnarrowed, but such an expansion or contraction of the channel can bearbitrarily made according to the design, and further it is necessarilynot an essential configuration.

In addition, the pressure chamber 20 of the discharge head 100 indicatesa space partitioned by the nozzle plate 10, the pressure chambersubstrate 120, and the vibration plate 30, and a space not including thenozzle hole 12 and the supply port 126. In other words, the pressurechamber 20 is a space of which the capacity is changed according to adisplacement of the vibration plate 30, and is defined as a space notincluding the narrowed channel communicating with the space or the like.

The ink supply chamber 40, the supply port 126, and the pressure chamber20 are partitioned by the nozzle plate 10, the pressure chambersubstrate 120, and the vibration plate 30. The ink supply chamber 40 cantemporarily store the ink supplied through a through hole 128 providedin the vibration plate 30 from the outside (for example, an inkcartridge). The ink within the ink supply chamber 40 can be supplied tothe pressure chamber 20 via the supply port 126. The capacity of thepressure chamber 20 changes according to the deformation of thevibration plate 30. The pressure chamber 20 communicates with the nozzlehole 12 and when the capacity of the pressure chamber 20 is changed, theink is discharged from the nozzle hole 12, or introduced into thepressure chamber 20 from the ink supply chamber 40.

In the discharge head 100, the vibration plate 30 is provided being incontact with the pressure chamber substrate 120. The vibration plate 30is deformed by an operation of the piezoelectric element 32, and it canchange the internal pressure of the pressure chamber 20 by changing thecapacity of the pressure chamber 20. In addition, in this example, thepressure chamber 20 is partitioned by the nozzle plate 10, the pressurechamber substrate 120, and the vibration plate 30. However, as long asthe capacity of the pressure chamber 20 can be changed according tovibration of the vibration plate 30, it is possible to form the pressurechamber by proper members, and the number, the shape, the material orthe like of the members for the pressure chamber are arbitrary.

In the discharge head 100, the piezoelectric element 32 is providedbeing in contact with the vibration plate 30. The piezoelectric element32 is electrically connected to a piezoelectric element driving circuit(not illustrated), and it can be operated (vibrated or deformed) basedon a signal of the piezoelectric element driving circuit. As thepiezoelectric element 32, it is not particularly limited, and forexample, a type of an element (an electromechanical conversion element)which is deformed by an application of a voltage can be exemplified. Inthe specification, a combination of a portion of the vibration plate 30partitioning the pressure chamber 20, and the piezoelectric element 32provided in the portion may be referred to as the piezoelectric actuator34. In addition, the vibration plate 30 may be integrally provided withelectrodes (for example, formed by Pt or the like) configuring thepiezoelectric element 32.

In the discharge head 100 of the embodiment, since a gap between thenozzle holes 12 is 127 μm or less, the piezoelectric element 32 ispreferably configured so that a piezoelectric material is disposedbetween the two electrodes. In other words, the piezoelectric actuator34 preferably has a thin film form in which one electrode, a layer ofthe piezoelectric material (for example, PZT (lead zirconate titanate)),and another electrode are sequentially laminated overall, with respectto the vibration plate 30. In addition, the volume (the capacity) of thepressure chamber 20 is 10.0×10⁶ μm³ or less.

A material of the vibration plate 30 is not particularly limited, andfor example, a laminate of layers formed of silicon oxide (SiO₂),silicon nitride (SiN), silicon oxide nitride (SiON), zirconium oxide(ZrO₂), titanium oxide (TiO₂), silicon carbide (SiC), and thesematerials or the like can be exemplified. As a material of the vibrationplate 30, a material having Young's modulus of 250 Gpa or less is morepreferable from a viewpoint that the vibration plate is greatlydisplaced, and damage hardly occurs. For example, it is more preferableto form the vibration plate including ZrO₂ (150 GPa), SiO₂ (75 GPa), Si(130 GPa), SUS (199 GPa), or Cr (248 GPa) (numbers within theparenthesis refer to Young's modulus). In addition, in a case where theelectrodes of the piezoelectric element 32 are formed by Pt, andintegrally laminated with the vibration plate 30, since Young's modulusof Pt is 168 GPa, and Young's modulus of ZrO₂ is 150 GPa, the vibrationplate may be configured as described above because the Young's modulusis 250 GPa or less even when they are combined.

In addition, in the specification, the Young's modulus refers to Young'smodulus measured in a static test (JIS G0567J or the like)(mechanicaltest), and for example, the Young's modulus is measured by using forexample, No. II-6 specimen.

The housing 130 can accommodate the nozzle plate 10, the pressurechamber substrate 120, and the piezoelectric element 32 as illustratedin FIG. 2. As a material of the housing 130, for example, a resin, ametal or the like can be exemplified. The housing 130 may have afunction of separating the piezoelectric element 32 from the outsideenvironment. In addition, an inert gas or the like may be sealed in thehousing 130, or the pressure inside the housing 130 may be reduced.According to this, it is possible to suppress deterioration or the likeof the piezoelectric material. In addition, the housing 130 is a covercovering the piezoelectric element 32, but a cover (not illustrated) maybe provided separately from the housing 130. In this case, the housing130 may function as a supporting body of the discharge head 100.

FIGS. 3 and 4 are cross-sectional schematic diagrams of main parts of adischarge head 101 and a discharge head 102 according to another exampleof the embodiment. In the description of the discharge head 101 and thedischarge head 102, the same reference numerals are used for the membershaving the same functions as in the discharge head 100 described above,and the detailed description is omitted.

Each of the discharge head 101 and the discharge head 102 illustrated inFIGS. 3 and 4 includes the plurality of pressure chambers 20respectively communicating with a plurality of nozzle holes 12 formed inthe nozzle plate 10, the vibration plate 30 changing each capacity ofthe plurality of pressure chambers 20, and the ink supply chamber 40supplying an ink to the plurality of pressure chambers 20.

FIGS. 3 and 4 schematically illustrate a flow of the ink from the inksupply chamber 40 to the nozzle hole 12 when an operation of dischargingthe ink is performed with dashed line arrows. A discharge port 127 isformed in the discharge head 101 illustrated in FIG. 3, and the pressurechamber 20 indicates a space partitioned by a channel formationsubstrate 110, the pressure chamber substrate 120, and the vibrationplate 30, and a space not including the nozzle hole 12, the dischargeport 127, and the supply port 126. In addition, in the discharge head102 illustrated in FIG. 4, the pressure chamber 20 indicates a spacepartitioned by the nozzle plate 10, the pressure chamber substrate 120,and the vibration plate 30, and a space not including the nozzle hole 12and the supply port 126. In other words, as in the description of thedischarge head 100 described above, in the discharge head 101 and thedischarge head 102, the pressure chamber 20 is a space of which thecapacity is changed according to a displacement of the vibration plate30, and is defined as a space not including the narrowed channelcommunicating with the space or the like. In both the discharge head 101and the discharge head 102, the capacity of the pressure chamber 20 is10.0×10⁶ μm³ or less, and the density of the arrangement of the nozzlehole 12 is 200 dpi or more.

In the discharge head 101 and the discharge head 102, a compliance sheet140 is used as a member forming a portion of the ink channel. Thecompliance sheet 140 is a flexible and elastic film. As long as thecompliance sheet 140 is an elastic film, the compliance sheet is notparticularly limited, and for example, a polymer film, a thin metalfilm, a glass fiber, a carbon fiber or the like can be exemplified. Amaterial of the polymer film is not particularly limited, and polyimide,nylon, polyolefin, polyphenylene sulfide or the like can be exemplified.In addition, as the metal, for example, materials including iron oraluminum can be exemplified.

The thickness of the compliance sheet 140 is not particularly limited,and for example, 50 μm or less is preferable, 20 μm or less is morepreferable, 1 μm to 10 μm is still more preferable. It is morepreferable to form the compliance sheet 140 with polyphenylene sulfide.When the compliance sheet 140 is too thin, a vibration occursconsiderably at the time of discharging the ink, and residual vibrationmay occur frequently. The compliance sheet 140 has a function of adamper for discharging or distributing the ink. In a case where thevolume of the ink is expanded, the compliance sheet 140 suppressesdamage to the discharge heads 101 and 102 by its deformation.

Both the discharge head 101 and the discharge head 102 have a cover 150.The cover 150 is configured as a member separate from the housing (notillustrated). The cover 150 is provided being in contact with thevibration plate 30, forms a space for accommodating the piezoelectricelement 32, and accommodates the piezoelectric element 32 in the space.A material of the cover 150 is the same as the material of the housing130 described above. The cover 150 may have a function of separating thepiezoelectric element from the outside environment, an inert gas or thelike may be sealed in the space formed by the cover 150, or the pressureinside the space may be reduced. According to this, it is possible tosuppress deterioration or the like of the piezoelectric material of thepiezoelectric element 32.

In a case where any one of the discharge heads 100, 101, and 102 of theembodiment exemplified in the above is mounted in the ink jet recordingapparatus, the nozzle plate 10 is disposed to face the recording paperP, and the nozzle plate 10 is in direct contact with the air (airoutside). Meanwhile, in a case where the discharge heads 100, 101, and102 of the embodiment have the housing 130 or the cover 150, thepiezoelectric element 32 and the vibration plate 30 are notsubstantially in contact with the air outside.

The ink jet recording apparatus is used with the ink introduced into thedischarge head. The ink jet recording apparatus is commonly used beinginstalled in an environment having a temperature close to roomtemperature. In a case where the ink jet recording apparatus isinstalled in a cold area, or in a case where an air conditioning devicein the installation environment fails, the temperature of the airoutside may be low (for example, 0° C. or less). In such a lowtemperature environment, in a case where the ink is an ink based onwater, the ink in the discharge head may become frozen, and thedischarge head may be damaged by the volume expansion of the ink causedby the freezing or the generation of ice. In particular, in thedischarge head of the embodiment, since the nozzle plate is configuredto be in direct contact with the air outside, the ink starts to becomefrozen from the vicinity of the nozzle plate within the channels in manycases. Thus, ice crystals become bigger, as it moves further away fromthe nozzle plate, and the piezoelectric element or the vibration plateare easily damaged. In other words, when the ink jet recording apparatusof the embodiment is cooled, and the ink is frozen, the ink of thenozzle plate side is preferentially frozen to the ink of the vibrationplate side within the pressure chamber of the discharge head.

In addition, in the discharge head of the embodiment, since the volumeof the pressure chamber 20 is 10.0×10⁶ μm³ or less, the density of thearrangement of the nozzle hole 12 is 200 dpi or more, and thepiezoelectric actuator 34, which is a thin film, is included, thepiezoelectric element or the vibration plate is easily damaged due tothe freezing of the ink. Further, in a case where the discharge head hasthe housing or the cover, a tendency in which the ink starts to becomefrozen from the nozzle plate side in the ink channel becomes remarkable.

Here, the ink jet recording apparatus of the embodiment uses the inkdescribed below. According to this, damage to the discharge head issuppressed. In addition, although the ink includes water as a component,it is possible to suppress the damage to the discharge head. In thefollowing, the ink is described.

1.2 Ink

The ink jet recording apparatus 200 of the embodiment discharges an inkdescribed below using the discharge head described above. The ink of theembodiment includes a dye, water, and an organic solvent. In addition, aratio (organic solvent/water) of a mass of the organic solvent to a massof water in the ink is 0.3 to 0.7. Hereinafter, the dye, water, andorganic solvent are sequentially described in detail.

1.2.1 Dye

The ink includes a dye. As the dye, it is not particularly limited, andvarious color pigments such as magenta, cyan, green, and yellow dye,which are generally used for an ink can be exemplified.

A content of the dye is preferably 0.1 mass % to 20 mass % with respectto the total mass of the ink, and more preferably 1 mass % to 15 mass %.By setting the content of the dye within the range described above, itis easy to obtain an image having excellent color development.

As the dye usable in the ink of the embodiment, for example, an acridinedye, an aniline dye, an anthraquinone dye, an azine dye, an azomethinedye, a benzo and naphthoquinone dye, an indioid dye, an indophenol dye,an indoaniline dye, an indamine dye, a leuco dye, a naphthalimide dye, anigrosine dye, an induline dye, a nitro and nitroso dye, an oxazine anddioxazine dye, an oxidation dye, a phthalocyanine dye, a polymethinedye, a quinophthalon dye, a sulfur dye, a tri and diacrylmethane dye, athiazine dye, a thiazole dye, a xanthane dye, a cyanin dye or the likecan be exemplified.

As the specific yellow-based dye, for example, C.I. Acid yellow 1, 3,11, 17, 19, 23, 25, 29, 36, 38, 40, 42, 44, 49, 59, 61, 70, 72, 75, 76,78, 79, 98, 99, 110, 111, 127, 131, 135, 142, 162, 164, 165, C.I. Directyellow 1, 8, 11, 12, 24, 26, 27, 33, 39, 44, 50, 58, 85, 86, 87, 88, 89,98, 110, 132, 142, 144, C.I. Reactive yellow 1, 2, 3, 4, 6, 7, 11, 12,13, 14, 15, 16, 17, 18, 22, 23, 24, 25, 26, 27, 37, 42, C.I. Food yellow3, 4, C.I. Solvent yellow, 15, 19, 21, 30, 109 or the like can beexemplified.

As the specific magenta-based dye, for example, C.I. Acid red 1, 6, 8,9, 13, 14, 18, 26, 27, 32, 35, 37, 42, 51, 52, 57, 75, 77, 80, 82, 85,87, 88, 89, 92, 94, 97, 106, 111, 114, 115, 117, 118, 119, 129, 130,131, 133, 134, 138, 143, 145, 154, 155, 158, 168, 180, 183, 184, 186,194, 198, 209, 211, 215, 219, 249, 252, 254, 262, 265, 274, 282, 289,303, 317, 320, 321, 322, C.I. Direct red 1, 2, 4, 9, 11, 13, 17, 20, 23,24, 28, 31, 33, 37, 39, 44, 46, 62, 63, 75, 79, 80, 81, 83, 84, 89, 95,99, 113, 197, 201, 218, 220, 224, 225, 226, 227, 228, 229, 230, 231,C.I. Reactive red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 15, 16, 17, 19,20, 21, 22, 23, 24, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41,42, 43, 45, 46, 49, 50, 58, 59, 63, 64, C.I. Solubilised red 1, C.I.Food red 7, 9, 14 or the like can be exemplified.

As the specific cyan-based dye, for example, C.I. Acid blue 1, 7, 9, 15,22, 23, 25, 27, 29, 40, 41, 43, 45, 54, 59, 60, 62, 72, 74, 78, 80, 82,83, 90, 92, 93, 100, 102, 103, 104, 112, 113, 117, 120, 126, 127, 129,130, 131, 138, 140, 142, 143, 151, 154, 158, 161, 166, 167, 168, 170,171, 182, 183, 184, 187, 192, 199, 203, 204, 205, 229, 234, 236, 249,C.I. Direct blue 1, 2, 6, 15, 22, 25, 41, 71, 76, 77, 78, 80, 86, 87,90, 98, 106, 108, 120, 123, 158, 160, 163, 165, 168, 192, 193, 194, 195,196, 199, 200, 201, 202, 203, 207, 225, 226, 236, 237, 246, 248, 249,C.I. Reactive blue 1, 2, 3, 4, 5, 7, 8, 9, 13, 14, 15, 17, 18, 19, 20,21, 25, 26, 27, 28, 29, 31, 32, 33, 34, 37, 38, 39, 40, 41, 43, 44, 46,C.I. Solubilised vat blue 1, 5, 41, C.I. Vat blue 4, 29, 60, C.I. Foodblue 1, 2, C.I. Basic blue 9, 25, 28, 29, 44 or the like can beexemplified.

As the specific dye of other color basis, for example, C.I. Acid green7, 12, 25, 27, 35, 36, 40, 43, 44, 65, 79, C.I. Direct green 1, 6, 8,26, 28, 30, 31, 37, 59, 63, 64, C.I. Reactive green 6, 7, C.I. Acidviolet 15, 43, 66, 78, 106, C.I. Direct violet 2, 48, 63, 90, C.I.Reactive violet 1, 5, 9, 10 or the like can be exemplified.

These dyes within a dye group of various color basis described above canbe used, and plural dyes selected from respective groups can be used.

1.2.2. Water

The ink of the embodiment includes water. In the ink of the embodiment,water is a main solvent. In other words, water is included in an amountof 50 mass % or more with respect to the total amount of the ink. Aswater, pure water such as ion exchange water, ultra-filtrated water,reverse osmotic water, distilled water or the like, or ultra pure watercan be used. In addition, by using water sterilized by ultravioletirradiation, hydrogen peroxide or the like, it is possible to preventmold or bacteria from being generated in a case where the inkcomposition is stored for a long period of time, which is preferable.

When the ink of the embodiment is frozen, the freezing of water causes avolume expansion. More specifically, when water in the ink is frozen,the volume of the water is increased by about 10%. In the ink of theembodiment, a volume expansion of water caused by the freezing is offsetby a volume contraction of the organic solvent, and the volume expansionof the entire ink is suppressed. Thus, damage to the vibration plate orthe piezoelectric element of the discharge head can be suppressed.

From this viewpoint, a ratio of the organic solvent described below towater in the ink of the embodiment is designed. Specifically, a ratio ofa mass of the organic solvent to a mass of the water in the ink (organicsolvent/water) is 0.3 to 0.7. In addition, as a value of the ratio, 0.35to 0.65 is preferable, and 0.4 to 0.6 is more preferable. By setting theratio as the above, it is possible to set the volume expansioncoefficient of the ink, in a case where the ink is frozen under atemperature condition of −20° C. within a range of 1.6% to 5.3%, and tosuppress damage to the vibration plate or the piezoelectric element.

1.2.3 Organic Solvent

The ink of the embodiment includes an organic solvent. The ink mayinclude various types of the organic solvent. In the ink, it ispreferable that the organic solvent becomes frozen later than water whena temperature is decreased. Therefore, as a melting point of the organicsolvent, −5° C. or less is preferable, and −10° C. or less is morepreferable.

As the organic solvent, it is not particularly limited, and for example,1,2-alkanediols, polyalcohols, pyrrolidone derivatives, lactone, glycolethers or the like can be exemplified.

As the 1,2-alkanediols, for example, 1,2-propanediol, 1,2-butanediol,1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol or the like can beexemplified. Since the 1,2-alkanediols are excellent in wetting arecording medium uniformly by increasing the wettability of the ink withrespect to the recording medium, an image having excellent adhesiveproperties on the recording medium may be formed. In a case where theink includes 1,2-alkanediols, it is possible to set a content of the1,2-alkanediols to 1 mass % to 20 mass % with respect to the total massof the ink.

As the polyalcohols, for example, ethylene glycol, diethylene glycol,triethylene glycol, propylene glycol, dipropylene glycol,1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,trimethylolpropane, glycerin or the like can be exemplified. Thepolyalcohols can be preferably used from a viewpoint of suppressingdrying and solidification of the ink and reducing clogging, dischargefailure or the like in a nozzle surface of a recording head of the inkjet recording apparatus. In a case where the ink includes thepolyalcohols, it is possible to set a content of the polyalcohols to 2mass % to 20 mass % with respect to the total mass of the ink.

As the pyrrolidone derivatives, for example, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-pyrrolidone,N-buthyl-2-pyrrolidone, 5-methyl-2-pyrrolidone,1-(2-hydroxyethyl)-2-pyrrolidone or the like can be exemplified. Thepyrrolidone derivatives can act as a preferable solvent of the resincomponent. In a case where the ink includes the pyrrolidone derivatives,it is possible to set a content of the pyrrolidone derivatives to 0.5mass % to 10 mass % with respect to the total mass of the ink.

In the invention, the “lactone” refers to a cyclic compound having anester group (—CO—O—) in the ring. As the lactone, as long as it fallsunder the definition described above, it is not particularly limited,and the lactone having a carbon number of 2 to 9 is preferable. Asspecific examples of this lactone, α-ethyl lactone, α-acetolactone,β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone,ζ-enantiolactone, η-caprylolactone, γ-valerolactone, γ-heptalactone,γ-nonalactone, β-methyl-δ-valerolactone, 2-buthyl-2-ethylpropiolactone,α,α-diethylpropiolactone or the like can be exemplified, and among theabove, γ-butyrolactone is particularly preferable. In a case where therecording medium is a film of a vinyl chloride resin or the like, thelactone causes the ink to infiltrate into the inside of the recordingmedium, thereby increasing the adhesive properties. It is possible toset the content of the lactone to 5 mass % to 30 mass % with respect tothe total mass of the ink.

As the glycol ethers, for example, ethylene glycol monoisobutyl ether,ethylene glycol monohexyl ether, ethylene glycol monoisohexyl ether,diethylene glycol monohexyl ether, triethylene glycol monohexyl ether,diethylene glycol monoisohexyl ether, triethylene glycol monoisohexylether, ethylene glycol monoisoheptyl ether, diethylene glycolmonoisoheptyl ether, triethylene glycol monoisoheptyl ether, ethyleneglycol monooctyl ether, ethylene glycol monoisooctyl ether, diethyleneglycol monoisooctyl ether, triethylene glycol monoisooctyl ether,ethylene glycol mono-2-ethylhexyl ether, diethylene glycolmono-2-ethylhexyl ether, triethylene glycol mono-2-ethylhexyl ether,diethylene glycol mono-2-ethylpentyl ether, ethylene glycolmono-2-ethylpentyl ether, ethylene glycol mono-2-ethylhexyl ether,diethylene glycol mono-2-ethylhexyl ether, ethylene glycolmono-2-methylpentyl ether, diethylene glycol mono-2-methylpentyl ether,tetraethylene glycol monobutyl ether, propylene glycol monobutyl ether,dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether,propylene glycol monopropyl ether, dipropylene glycol monopropyl ether,tripropylene glycol monomethyl ether or the like can be exemplified.Among the above, one type can be used singly, or two or more types canbe used in combination. The glycol ethers can suppress wettability or aninfiltration rate of the ink with respect to the recording medium.Therefore, it is possible to record a clear image having littlegradation unevenness. In a case where a water-based ink is used, and theink includes glycol ethers, it is possible to set a content of theglycol ethers to 0.05 mass % to 40 mass % with respect to the total massof the ink.

The volume of the organic solvent is reduced along with a decrease intemperature. In the ink of the embodiment, an increase of the volumecaused when water in the ink is frozen is absorbed by a reduction of thevolume of the organic solvent, and an increase of the entire volume ofthe ink is suppressed. From this viewpoint, a ratio of an organicsolvent described below to water in the ink of the embodiment isdesigned. Specifically, a ratio of a mass of the organic solvent to amass of the water in the ink (organic solvent/water) is 0.3 to 0.7. Inaddition, as a value of the ratio, 0.35 to 0.65 is preferable, and 0.4to 0.6 is more preferable. By setting the ratio as the above, it ispossible to set the volume expansion coefficient of the ink, in a casewhere the ink is frozen under a temperature condition of −20° C. withina range of 1.6% to 5.3%.

1.2.4 Other Components

The ink of the embodiment may include components such as a surfactant, asolid moisturizing agent, a pH adjuster, a preservative, a fungicide, arust-preventive agent, a chelating agent, a pigment or the like, inaddition to the components described above.

The ink of the embodiment includes a resin component. As the resincomponent, a type of a resin improving physical strength such asabrasion resistance of an image to be recorded (may be referred to as afixing resin), a resin adjusting viscosity of the ink as a thickener, atype of a resin dispersing the pigment or the like can be exemplified.

As a more specific resin component, well known resins such as anacrylic-based resin, a styrene acrylic-based resin, a fluorene-basedresin, a urethane-based resin, a polyolefin-based resin, a rosinmodified resin, a terpene-based resin, a polyester-based resin, apolyamide-based resin, an epoxy-based resin, a vinyl chloride-basedresin, a vinyl chloride-vinyl acetate copolymer, and a ethylene aceticacid vinyl-based resin; polyolefin wax, or the like can be exemplified.One type of the resin can be used singly, or two or more types thereofcan be used in combination. In addition, among the exemplified resins,the styrene acrylic-based resin, the polyester-based resin, and thepolyolefin wax can be preferably used.

As the polyester-based resin, a commercially available product can beused. For example, Eastek 1100, 1300, 1400 (all of the above are tradenames, manufactured by Eastman Chemical Company), elitel KA-5034,KA-3556, KA-1449, KT-8803, KA-5071S, KZA-1449S, KT-8701, KT9204 (all ofthe above are trade names, manufactured by UNITIKA LTD) or the like canbe exemplified.

As the styrene acrylic-based resin, for example, a styrene-acrylic acidcopolymer, a styrene-methacrylic acid copolymer, a styrene-methacrylicacid-acrylate copolymer, a styrene-α-methylstyrene-acrylic acidcopolymer, a styrene-α-methylstyrene-acrylic acid-acrylate copolymer orthe like can be exemplified. In addition, as an aspect of the copolymer,any aspects of a random copolymer, a block copolymer, an alternatingcopolymer, and a graft copolymer can be used. In addition, as thestyrene acrylic-based resin, a commercially available product may beused. As the commercially available product of the styrene acrylic-basedresin, JONCRYL 62J (manufactured by BASF Japan Ltd.) or the like can beexemplified.

As the polyolefin wax, it is not particularly limited, and for example,a wax manufactured from olefin such as ethylene, propylene, butylene orthe like, or derivatives thereof; and a copolymer thereof, specifically,a polyethylene-based wax, a polypropylene-based wax, apolybutylene-based wax or the like can be exemplified. Among the above,from a viewpoint of reducing generation of cracks of an image, thepolyethylene-based wax is preferable. One type of the polyolefin wax canbe used singly, or two or more types thereof can be used in combination.

As a commercially available product of the polyolefin wax, CHEMIPEARLseries such as “CHEMIPEARL W4005” (manufactured by Mitsui Chemicals,Inc., polyethylene-based wax, particle diameter of 200 nm to 800 nm,softening point of 110° C. by a ring and ball method, hardness of 3 by apenetration method, solid content of 40%) or the like can beexemplified. In addition to the above, AQUACER series such as AQUACER513 (polyethylene-based wax, particle diameter of 100 nm to 200 nm,melting point of 130° C., solid content of 30%), AQUACER 507, AQUACER515, AQUACER 539, and AQUACER 593, AQUACER 840 (all of the above aremanufactured by BYK Japan KK), Hitech series such as Hitech E-7025P,Hitech E-2213, Hitech E-9460, Hitech E-9015, Hitech E-4A, HitechE-5403P, and Hitech E-8237 (all of the above are manufactured by TOHOChemical Industry Co., Ltd), Nopcoat PEM-17 (manufactured by SAN NOPCOLIMITED, polyethylene emulsion, particle diameter of 40 nm) or the likecan be exemplified. These are commercially available in the form of awater-based emulsion in which a polyolefin wax is dispersed in water bya common method.

In addition, as the urethane-based resin, any types of an emulsion typedispersed in a particle shape in a solvent, and a solvent type existingin a dissolved state in the solvent may be used. In addition, theemulsion type can be classified into a forced emulsification type and aself emulsification type depending on its emulsification method, and itis possible to use any type of the emulsification in the embodiment, butthe self emulsification type is preferable. Since a dispersion of theself emulsification type is excellent in film forming properties orwater resistance compared with the forced emulsification type, it ispossible to perform a printing which is even stronger to water.

As the polyurethane-based resin used in the embodiment, for example, aforced emulsification type polyurethane emulsion such as “TAKELAC(registered trademark) W-6061” (manufactured by Mitsui Chemicals, Inc.)or the like, and a self emulsification type emulsion such as “RESAMINE(registered trademark) D-1060” (manufactured by DainichiseikaColor&Chemicals Mfg. Co., Ltd.), “TAKELAC W-6021” (manufactured byMitsui Chemicals, Inc.), “WBR-016U (polyether manufactured by TAISEIFINE CHEMICAL CO., LTD., Tg=20° C.) or the like can be exemplified.

In a case where the emulsion type described above is used as thepolyurethane resin, an average particle diameter of the polyurethaneresin is preferably 50 nm to 200 nm, and more preferably 60 nm to 200nm. When the average particle diameter of the polyurethane resin is inthe range described above, it is possible to disperse the polyurethaneresin particles in the ink uniformly.

As the fixing resin of a water-based emulsion forms a resin film,preferably with a wax, the ink is fixed on the medium to be recordedsufficiently, and an effect of enhancing adhesive properties andabrasion resistance of the image is exhibited. According to the abovedescribed effect, an article recorded by using a coloring ink includinga resin emulsion has excellent abrasion resistance against the medium tobe recorded.

In addition, the resin emulsion functioning as a binder is included inthe ink in a state of an emulsion. When the resin functioning as abinder is included in the ink in a state of an emulsion, it is easy toadjust viscosity of the ink to a proper range in an ink jet recordingmethod, and storage stability and discharge stability of the coloringink become excellent.

As the resin emulsion, it is not limited as follows, but for example, ahomopolymer or copolymer of (meth)acrylic acid, (meth)acrylic acidester, acrylonitrile, cyanoacrylate, acrylamide, olefin, styrene, vinylacetate, vinyl chloride, vinyl alcohol, vinyl ether, vinyl pyrrolidone,vinyl pyridine, vinyl carbazole, vinyl imidazole, and vinylidenechloride, a fluorine resin, a natural resin or the like can beexemplified. Among the above, at least any one of a (meth)acrylic-basedresin and styrene-(meth)acrylic acid copolymer-based resin ispreferable, at least any one of a acrylic-based resin andstyrene-acrylic acid copolymer-based resin is preferable, andstyrene-acrylic acid copolymer-based resin is further preferable. Inaddition, the above described copolymer may be any forms of a randomcopolymer, a block copolymer, an alternating copolymer, and a graftcopolymer. Among the above, a urethane-based resin is preferable, and inparticular, water-soluble polyurethane is preferable. As the preferablespecific example of the water-soluble polyurethane resin, NeoRezR-960(manufactured by AstraZeneca), NeoRezR-989 (manufactured byAstraZeneca), NeoRezR-9320 (manufactured by AstraZeneca), NeoRadNR-440(manufactured by AstraZeneca), HYDRAN AP-30 (manufactured by DICCorporation), HYDRAN APX-601 (manufactured by DIC Corporation), HYDRANSP-510 (manufactured by DIC Corporation), HYDRAN SP-97 (manufactured byDIC Corporation), ELASTRON MF-60 (manufactured by DSK Co., Ltd.),ELASTRON MF-9 (manufactured by DSK Co., Ltd.), M-1064 (manufactured byDSK Co., Ltd.), IzelaxS-1020 (manufactured by HODOGAYA CHEMICAL CO.,LTD.), IzelaxS-1040 (manufactured by HODOGAYA CHEMICAL CO., LTD.),IzelaxS-1085C (manufactured by HODOGAYA CHEMICAL CO., LTD.),IzelaxS-4040N (manufactured by HODOGAYA CHEMICAL CO., LTD.), NEOTANUE-5000 (manufactured by TOGASEI CO., LTD), RU-40 series (manufacturedby Style Japan), U-COAT UWS-145 (manufactured by Sanyo Chemicalindustries, Ltd), PERMARIN UA-150 (manufactured by Sanyo Chemicalindustries, Ltd), WF-series (manufactured by Style Japan), and WPC-101(manufactured by Nippon Polyurethane Industry Co., Ltd) can beexemplified.

As the resin emulsion, a commercially available product may be used, andthe resin emulsion may be manufactured by using an emulsionpolymerization method as follows. As a method for obtaining athermoplastic resin in the ink in a state of an emulsion, a method ofemulsion polymerizing a monomer of the water-soluble resin describedabove in water in which a polymerization catalyst and an emulsifierexist can be exemplified. A polymerizing initiator, an emulsifier, and amolecular weight adjuster used in the emulsion polymerization can beused according to the well known method in the related art.

In order to further improve the storage stability and dischargestability of the ink, an average particle diameter of the resin emulsionis preferably in a range of 5 nm to 400 nm, and more preferably in arange of 20 nm to 300 nm.

In addition, as the resin component imparting viscosity to the ink, forexample, polyvinyl alcohols, poly(meth)acrylic acids, polyethers,polyvinyl pyrrolidones, polyvinyl formals, proteins (for example,gelatin, casein, glue or the like), polysaccharides (for example,pullulan, dextran, dextrin, cyclodextrine, carrageenan, pectin,glucomannan, sodium alginate, xanthan gum, arabic gum, locust bean gum,tragacanth gum, guar gum, tamarind gum or the like), starches (forexample, starch, oxidized starch, carboxyl starch, dialdehyde starch orthe like), cellulose or derivatives thereof (for example, methylcellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethylcellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose or thelike), an alginate salt (for example, sodium alginate, potassiumalginate, ammonium alginate or the like), alginate (for example,propylene glycol alginate or the like) or the like can be exemplified.

When the resin component described above is included in the ink of theembodiment, it is preferable to blend the resin component in the ink ofthe embodiment as a solid content in an amount of 1.5 mass % or morewith respect to the total mass of the ink, regardless of a function orthe type of the resin component. According to this, the ice (icecrystal) formed by the freezing of water in the ink can be more refined,and softened. According to this, when the ink is frozen, since it ispossible to form a so-called sherbet shape, it is possible to contributeto suppressing damage to the vibration plate or piezoelectric element ofthe discharge head described above.

In addition, as the resin component, a resin having high softness ispreferably used, and a resin having a glass transition temperature (Tg)of 80° C. or less, preferably 75° C. or less, more preferably 50° C. orless is preferably used.

The surfactant have a function of decreasing surface tension andimproving wettability with respect to a acetylene glycol-basedsurfactant, a silicone-based surfactant, and a fluorine-based surfactantcan be preferably used.

As the acetylene glycol-based surfactant, it is not particularlylimited, and for example, Surfynol 104, 104E, 104H, 104A, 104BC, 104DPM,104PA, 104PG-50, 104S, 420, 440, 465, 485, SE, SE-F, 504, 61, DF37,CT111, CT121, CT131, CT136, TG, GA, DF110D (all of the above are tradenames, manufactured by Air Products and Chemicals. Inc.), Olfine B, Y,P, A, STG, SPC, E1004, E1006, E1008, E1010, PD-001, PD-002W, PD-003,PD-004, EXP.4001, EXP.4036, EXP.4051, EXP.4300, AF-103, AF-104, AK-02,SK-14, AE-3 (all of the above are trade names, manufactured by NissinChemical Co., Ltd), Acetylenol E00, E00P, E40, and E100 (all of theabove are trade names, manufactured by Kawaken Fine Chemicals Co., Ltd)can be exemplified.

As the silicone-based surfactant, it is not particularly limited, and apolysiloxane-based compound can be preferably exemplified. As thepolysiloxane-based compound, it is not particularly limited, and forexample, a polyether modified organosiloxane can be exemplified. As acommercially available product of the polyether modified organosiloxane,for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346,BYK-348, BYK-349 (all of the above are trade names, manufactured byBYK), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945,KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015,and KF-6017 (all of the above are trade names, manufactured by Shin-EtsuChemical Co., Ltd) can be exemplified.

As the fluorine-based surfactant, a fluorine modified polymer ispreferably used, and as a specific example, BYK-340 (manufactured by BYKJapan KK) can be exemplified.

When the ink includes a surfactant, a content thereof is preferably 0.1mass % to 1.5 mass % with respect to the total mass of the ink.

An agent having a melting point of 20° C. or more, and solubility towater of 5 mass % or more at 20° C. corresponds to the solidmoisturizing agent. Specifically, alcohols such as 1,4-butanediol,2,3-butanediol, 2-ethyl-2-(hydroxymethyl)-1,3-propandiol or the like,esters such as ethylene carbonate or the like, nitrogen compounds suchas acetamide, N-methyl acetamide, 2-pyrrolidone, ε-caprolactam, urea,thiourea, N-ethyl urea or the like, and saccharides such asdihydroxyacetone, erythritol, D-arabinose, L-arabinose, D-xylose,2-deoxy-β-D-ribose, D-lyxose, L-lyxose, D-ribose, D-arabitol, ribitol,D-altrose, D-allose, D-galactose, L-galactose, D-quinovose, D-glucose,D-digitalose, D-digitoxose, D-cymarose, L-sorbose, D-taggatose,D-talose, 2-deoxy-D-glucose, D-fucose, L-fucose, D-fructose, D-mannose,L-rhamnose, D-inositol, myo-inositol, D-glucitol, D-mannitol,methyl=D-galactopyranoside, methyl=D-glucopyranoside,methyl=D-mannopyranoside, N-acetyl chitobiose, isomaltose, xylobiose,gentiobiose, kojibiose, chondrosine, sucrose, cellobiose, sophorose,α,α-trehalose, maltose, melibiose, lactose, laminaribiose, rutinose,gentianose, stachyose, cellotriose, planteose, maltotriose, melezitose,lacto-N-tetraose, raffinose or the like can be exemplified.

When the solid moisturizing agent is added, it is preferable to add thesolid moisturizing agent in an amount of 80 mass % or less with respectto the total mass of water, from a viewpoint of preventing the agentfrom being precipitated prior to the freezing of water, when theapparatus is cooled.

As the pH adjuster, for example, potassium dihydrogenphosphate, disodiumhydrogenphosphate, sodium hydroxide, lithium hydroxide, potassiumhydroxide, ammonia, diethanolamine, triethanolamine,triisopropanolamine, potassium carbonate, sodium carbonate, sodiumhydrogen carbonate or the like can be exemplified.

As the preservative and the fungicide, for example, sodium benzoate,pentachlorophenol sodium, 2-pyridinethiol-1-oxide sodium, sodiumsorbate, sodium dehydroacetate, and 1,2-dibenzothiazoline-3-one can beexemplified. As a commercially available product, PROXEL XL2, PROXEL GXL(all of the above are trade names, manufactured by Avecia), DenicideCSA, NS-500W (all of the above are trade names, manufactured by NagaseChemteX Corporation) or the like can be exemplified.

As the rust-preventative agent, for example, benzotriazole can beexemplified. In addition, as the chelating agent, for example,ethylenediaminetetraacetic acid and salts thereof(ethylenediaminetetraacetic acid dihydrogen disodium salt or the like),(S,S)-ethylenediamine disuccinic acid and salts thereof, dicarboxymethylglutamic acid and salts thereof, iminodisuccinic acid and salts thereof(iminodisuccinic acid tetrasodium) or the like can be exemplified.

As the pigment which can be blended in the ink of the embodiment, it isnot particularly limited, but various color pigments such as magenta,cyan, green, and yellow pigment, white pigments, bright pigments or thelike, which are generally used for an ink can be exemplified. Inaddition, among the above, the self dispersion type pigment may be used.Further, when a common pigment is used, it is preferable to blend itwith the dispersion resin described above, and the dispersion resin mayfunction as the resin component.

1.3 Operational Effect

The ink jet recording apparatus of the embodiment includes the inkdescribed above, and the discharge head described above. The capacity ofthe pressure chamber of the discharge head is 10.0×10⁶ μm³ or less, thedensity in which the plurality of nozzle holes are arranged in thenozzle plate is 200 dpi or more, and the ink jet recording apparatusincludes a highly dense and miniaturized discharge head. However, sincethe ink jet recording apparatus uses an ink in which a ratio of theorganic solvent to water described above is 0.3 to 0.7, damage to thedischarge head caused by the freezing of the ink hardly occurs even whenthe apparatus is placed in a low temperature environment.

In other words, in such ink jet recording apparatus, at least a part ofvolume expansion caused by solidification of water in a case where theapparatus is placed in a low temperature environment is offset by volumecontraction of the organic solvent. According to this, it is possible toreduce stress which may damage the vibration plate or piezoelectricelement of the discharge head.

2. Examples, Comparative Examples and Reference Examples

Hereinafter, Examples, Comparative Examples and Reference Examples areillustrated, and the invention is further described. However, theinvention is not limited at all by the following examples.

2.1 Adjustment of Ink

Materials shown in Table 1 were put into a container, mixed and stirredfor 2 hours by a magnetic stirrer. After that, impurities such as wastesor coarse particles were removed by filtering the mixture by a membranefilter having a pore diameter of 5 μm, thereby preparing each ink usedfor Examples, Comparative Examples and Reference Examples. In addition,numerical values in Table 1 show mass %, and water (ion exchange water)was added such that the total mass of the ink is 100 mass %.

TABLE 1 Ink 1 Ink 2 Ink 3 Ink 4 Ink 5 Ink 6 Ink 7 Cyan dye 4.5 1.0 2.02.0 Yellow dye 8.0 2.0 1.0 Glycerin 9.0 10.0 10.0 12.0 9.0 12.0 9.0Triethylene glycol 9.0 6.0 2.0 9.0 2.0 8.0 2.0 2-pyrrolidone 3.0 9.0 1.01.0 1.0 1.0 1.0 Urea 2.0 Polyethylene glycol 2.0 3.0 3.0 2.0 3.0 2.0mono-2-ethylhexyl ether Triethylene glycol 6.0 10.0 6.5 7.0 7.0 7.0 7.0monobutyl ether 1,2-hexanediol 1.0 Olfine E1010 0.5 1.0 2.0 0.5 1.0 0.51.0 Fixing resin (Tg 0° C., average particle 1.5 10.0 diameter 100 nm)Water 65.0 54.0 74.5 65.5 74.5 57.5 76.0 Total amount of 30.5 38.0 24.532.5 22.0 31.5 22.0 organic solvent Total amount 100.0 100.0 100.0 100.0100.0 100.0 100.0 Ratio of total amount 0.47 0.70 0.33 0.50 0.30 0.550.29 of organic solvent/water Volume expansion 3.45% 1.60% 5.00% 3.30%5.25% 2.60% 5.40% coefficient due to freezing of ink

Each of the materials shown in Table 1 is as follows.

(Coloring Material)

Cyan(C) dye (C.I. Direct blue 199)

Magenta(C) dye (C.I. Direct yellow 132)

(Fixing Resin)

Urethane resin (trade name “M-1064”, manufactured by DKS Co., Ltd)

(Alkylpolyols)

1,2-hexanediol (normal boiling point: 224° C., log P value: 0.50)

glycerin (normal boiling point: 290° C., log P value: −2.70)(Moisturizing agent)

urea

(Pyrrolidone Derivatives)

2-pyrrolidone

(Surfactant)

Olfine E1010 (acetylene glycol-based surfactant)

(Others)

TEGmBE: triethylene glycol monobutyl ether

In addition, the total amount of the organic solvent, a ratio of themass of the organic solvent to the mass of water (organicsolvent/water), and a theoretical value of volume expansion coefficientof the entire ink when the ink is frozen are written in combination.

2.2 Evaluation Test

A plurality of ink jet recording apparatuses having different dischargeheads were prepared. Each discharge head included in each of the ink jetrecording apparatuses is referred to as a head A, a head B, a head C,respectively.

In the head A, a nozzle arrangement density is 300 dpi, and the capacityof the pressure chamber is 2.9×10⁶ μm³.

In the head B, a nozzle arrangement density is 360 dpi, and the capacityof the pressure chamber is 3.7×10⁶ μm³.

In the head C, a nozzle arrangement density is 180 dpi, and the capacityof the pressure chamber is 14.4×10⁶ μm³.

In addition, as shown in Table 2, the ink jet recording apparatusincluding the predetermined discharge head was filled with the ink shownin Table 1 to be capable of printing, and the entire ink jet recordingapparatus was placed in a freezing room of which the temperature was setto −20° C. After 5 days passed, the ink jet recording apparatus wastaken out of the freezing room, and returned to room temperatureenvironment. After that, a printing evaluation was performed, in a casewhere image disturbance and dot omission occurred, the head was takenout of the ink jet recording apparatus, and it was observed whether thepiezoelectric actuator was damaged or not with a microscope.

As a result of the observation, in a case in which image disturbance anddot omission did not occur and the piezoelectric actuator was notdamaged is indicated by A, and in a case in which cracks or the likeoccurred in the piezoelectric actuator is indicated by B, and the resultis shown in Table 2.

TABLE 2 Comparative Reference Examples Examples Example 1 2 3 4 5 6 1 21 Ink type 1 2 3 4 5 6 7 4 7 (refer to Table 1) Head A A A A A A A AHead B A Head C A Whether A A A A A A B B A piezoelectric actuator isdamaged or not

2.3 Evaluation Result

When Table 2 is referred to, in Examples 1 to 6, with regard to the headA, it is determined that the discharge head was not damaged, in a casewhere a composition ratio of the ink (organic solvent/water) was 0.3 to0.7. In contrast to this, in Comparative Example 1, a composition ratioof the ink (organic solvent/water) was 0.3 or less, and the dischargehead was damaged. It is considered that this is because the volumeexpansion amount of water caused by the freezing is greater than thevolume contraction amount of organic solvent. In addition, inComparative Example 2, although a composition ratio of the ink (organicsolvent/water) was 0.3 to 0.5, the discharge head was damaged.

It is considered that this is because, since the capacity of thepressure chamber of the used head C exceeds 10×10⁶ μm³, even if a partof the volume expansion amount of water caused by the freezing is offsetby the volume contraction amount of organic solvent, the entire volumeexpansion amount is not suppressed.

Meanwhile, Reference Example 1 is a combination of the head B and theink 7. Although a composition ratio of the ink (organic solvent/water)was 0.3 or less, the discharge head was not damaged. A structure of thehead B was as illustrated in FIG. 4, the ink of the head B started tobecome frozen from a nozzle, next the pressure chamber became frozen,and the freezing stopped in the ink supply chamber. However, it isconsidered that since the pressure caused by the ink expansion at thetime of freezing can escape to an upstream side of the channel, thepressure chamber having low intensity is not damaged.

The invention is not limited to the embodiment described above, and canbe modified in various ways. For example, the invention includes theconfiguration (for example, a configuration having the same function,method, and result, or a configuration having the same purpose andeffect) substantially the same as the configuration described in theembodiment. In addition, the invention includes a configuration of whicha nonessential portion of the configuration described in the embodimentis substituted. In addition, the invention includes a configurationhaving the same operational effect as the configuration described in theembodiment, or a configuration which can achieve the same purpose as theconfiguration described in the embodiment. In addition, the inventionincludes a configuration in which a well known technology is added tothe configuration described in the embodiment.

The entire disclosure of Japanese Patent Application No. 2014-164203,filed Aug. 12, 2014 is expressly incorporated by reference herein.

What is claimed is:
 1. An ink jet recording apparatus comprising: anink; and a discharge head that discharges the ink, wherein the dischargehead includes a plurality of pressure chambers respectivelycommunicating with a plurality of nozzle holes formed in a nozzle plate,a vibration plate changing the capacity of each of the plurality ofpressure chambers, and an ink supply chamber for supplying the ink tothe plurality of pressure chambers, the capacity of the pressure chamberis 10.0×10⁶ μm³ or less, and the density in which the plurality ofnozzle holes are arranged in the nozzle plate is 200 dpi or more, andwherein the ink includes a dye, water, and an organic solvent, a ratio(organic solvent/water) of a mass of the organic solvent to a mass ofthe water in the ink is 0.3 to 0.7.
 2. The ink jet recording apparatusaccording to claim 1, wherein when the ink jet recording apparatus iscooled, and the ink is frozen, an ink of the nozzle plate side ispreferentially frozen to the ink of the vibration plate side within thepressure chamber.
 3. The ink jet recording apparatus according to claim1, wherein the pressure chamber and the vibration plate is notsubstantially in contact with the air outside.
 4. The ink jet recordingapparatus according to claim 1, wherein Young's modulus of a materialconfiguring the vibration plate is 250 Gpa or less.
 5. The ink jetrecording apparatus according to claim 1, wherein a flexible and elasticfilm is included in a portion of a wall surface of the ink supplychamber.
 6. The ink jet recording apparatus according to claim 1,wherein a volume expansion coefficient of the ink in a case where theink is frozen under a temperature condition of −20° C. is 1.6% to 5.3%.7. The ink jet recording apparatus according to claim 1, wherein the inkincludes a resin component.